This invention relates to a method of producing polycarbonate by an interfacial polycondensation process wherein the polycarbonate is formed as particulates by using a low organic to aqueous phase volume ratio. More particularly, this invention relates to an improved interfacial polycondensation polycarbonate process which does not require large quantities of strong base to produce a particulate product.
Interfacial polycondensation processes wherein the polycarbonate is formed as particulates in the liquid aqueous phase have been reported previously in U.S. Pat. Nos. 4,368,315 and 4,360,659, assigned to the same assignee as the present invention, the contents of which are incorporated herein by reference. The procedures outlined in these references utilize an agitated two-phase reaction solvent medium containing a liquid inert organic solvent phase and a liquid aqueous phase in a volume ratio within the range of from 0.04:1 to 0.20:1 during the preparation of an aromatic polycarbonate from a dihydroxy aromatic compound and carbonyl halide. These processes provide the benefits of (1) utilizing reduced amounts of inert organic solvent during the polycondensation process and (2) eliminate or reduce the use of (a) an anti-solvent in the separation and recovery of polycarbonate from the reaction environment and/or (b) steam precipitation to recover polycarbonate from the organic phase. This is permitted since substantially all the polycarbonate formed precipitates in situ in the aqueous phase.
While these processes have provided acceptable aromatic polycarbonates, there still remains room for improvement. For example, when the organic to aqueous phase ratio is about 0.05 the polycarbonate often precipitates as agglomerated solids or sticky globs rather than fine particles unless the mole ratio of strong base to aromatic dihydroxy compound is at a value of 4.0 or above. In producing polycarbonate it is desirable to maintain caustic soda usage at a minimum to reduce costs and avoid degradation of the polymer. It is a disadvantage to employ 4 moles of base per mole of aromatic dihydroxy compound when considering that interfacial polycondensation polycarbonate processes which utilize high organic to aqueous phase volume ratios provide a suitable product upon steam precipitation with less than 3 moles of base per mole of aromatic dihydroxy compound. This invention overcomes this disadvantage and does not require large quantities of base to avoid the agglomeration or glob formation of the polycarbonate product. The quantity of strong base utilized in this process relative to aromatic dihydroxy compound can be reduced to a ratio less than 4.0 with no glob formation.